There is no definitive answer to this question as it depends on a number of factors, including the individual's height and body proportions. However, based on the available evidence, it is safe to say that the largest head in the world belongs to Robert Wadlow, who was born in 1918 and measured 8 feet 11.1 inches tall at his death in 1940. Wadlow's head circumference was an astonishing 25 inches - almost double that of an average adult male today.
While Wadlow's head size may be unmatched in modern times, there are reports of larger heads throughout history. For example, Chang and Eng Bunker - better known as the original Siamese Twins - were born in 1811 and measured 8 feet 3 inches tall. Their heads were said to be so large that they could not wear normal-sized hats or lie down side by side on a pillow.
Another notable individual with an unusually large head was Frenchwoman Jeanne Calment, who lived to be 122 years old and holds the record for oldest person ever documented. Calment's head circumference was 24 inches - just one inch shy of Wadlow's record-setting measurement.
So while there is no clear cut answer as to who has the largest head in the world, based on available evidence it seems safe to say that Robert Wadlow holds this title.